Measurement of the water content of a solution has conventionally been conducted by utilizing Karl Fischer's reaction, which was discovered by Karl Fischer. The conventionally employed electrolytic solution for Karl Fischer's coulometric titration generally comprises the following components (i) to (iv):
(i) Iodine or an iodide PA1 (ii) Sulfur dioxide PA1 (iii) Pyridine PA1 (iv) Solvent
The solvents for the electrolytic solution which have so far been employed include alcohols, e.g., methanol, ethanol, chloroform, propylene carbonate, and the like.
When using methanol as the solvent (iv), the reaction between the electrolytic solution for Karl Fischer's (hereinafter KF) coulometric titration and water proceeds as follows: EQU SO.sub.2 +I.sub.2 +H.sub.2 O+3C.sub.5 H.sub.5 N.fwdarw.2C.sub.5 H.sub.5 N.HI+C.sub.5 H.sub.5 N.SO.sub.3 ( 1) EQU C.sub.5 H.sub.5 N.SO.sub.3 +CH.sub.3 OH.fwdarw.C.sub.5 H.sub.5 N.HSO.sub.4 CH.sub.3 ( 2)
According to KF coulometric titration, iodine in the above-described formula (1) is internally formed by electrolytic oxidation of an iodide ion, and the thus formed iodine and water are allowed to react. The water content in a sample to be analyzed can be determined by the amount of iodine generated. More specifically, measurement of the water content of a sample can be carried out by charging the electrolytic solution (anolyte) in an anode chamber and an appropriate catholyte in a cathode chamber, passing an electric current therethrough to previously remove the water content of the anolyte, supplying a sample to be analyzed to the electrolyte, and again passing a current therethrough to titrate the water content of the sample. When using iodine in the preparation of the electrolytic solution, the above operation is followed, after water is added to the electrolytic solution, until the iodine color disappears.
In recent years, pyridine as the component (iii) has been replaced by imidazole as taught in Japanese Patent Application (OPI) No. 137250/81 (the term "OPI" herein used means "published unexamined application") due to the peculiar offensive smell of pyridine.
However, when these conventional electrolytic solutions are applied to measuring the water content of a solid sample, that is not dissolved in an electrolytic solution, by means of a water content vaporization apparatus, the solvent may vaporize during measurement to cause precipitation of a solid, thus giving rise to the following problems. That is, a commercially available KF coulometric titration apparatus and a commercially available water content-vaporization apparatus are connected, for example, as shown in FIG. 1. Electrolytic solution (anolyte) (18) is placed in an anode chamber of titration vessel (2) of KF coulometric titration apparatus (1), and an appropriate catholyte is placed in a cathode chamber, followed by passing an electric current therethrough to remove water in the anolyte. In the vaporization apparatus (4), the water content of a solid sample is vaporized according to an operating procedure for the apparatus. Specifically, a solid sample (8) is fed into boat (7) placed in heating tube (6) from sample feeder (10) through outlet (9), and the boat is then pushed into heating furnace (5) by pusher (11). The water content in the sample is vaporized by heating while controlling the temperature inside heating furnace (5) by means of temperature controller (15). The water vapor is driven out of the funnel together with carrier gas (19), e.g., nitrogen, which is introduced into heating furnace (5) through drying tubes (12) and (13) containing a desiccant, e.g., phosphorus pentoxide (16) or silica gel (17). The amount of the carrier gas to be introduced is controlled by means of flow meter (14). The water vapor is blown into electrolyte (18) in titration vessel (2) via blowing tube (3), wherein the water is titrated by means of coulometer (1).
In the above-described operation, the solvent in the electrolytic solution is vaporized away in the neighborhood of the blowing tube during the water content measurement. As a result, oil droplets or a solid precipitate is attached to the inner wall of the blowing tube connecting the vaporization apparatus and the titration vessel, and the water from the sample is adsorbed thereon, which results in a tendency to lower the water content measured. Even if the adsorbed water is desorbed, desorption not only takes time but also fails to assure accuracy of the measurement and, in addition, deteriorates reproducibility.